How to replace specific values in a dataset with randomized numbers?

I have a data column that contains a bunch of ranges as strings (e.g. "2 to 4", "5 to 6", "7 to 8" etc.). I'm trying to create a new column that converts each of these values to a random number within the given range. How can I leverage conditional logic within my function to solve this problem?

I think the function should be something along the lines of:

df<-mutate(df, c2=ifelse(df$c=="2 to 4", sample(2:4, 1, replace=TRUE), "NA"))

Which should produce a new column in my dataset that replaces all the values of "2 to 4" with a random integer between 2 and 4, however, this is not working and replacing every value with "NA".

Ideally, I am trying to do something where the dataset:

df<-c("2 to 4","2 to 4","5 to 6")

Would add a new column:

df<-c2("3","2","5")

Does anyone have any idea how to do this?